1. Field of the Invention
The present invention relates to a plate, and more particularly to a plate adapted to eutectic bonding a light emitting diode (LED) chip.
2. Description of Related Art
As the environment protection consciousness rises nowadays, in addition to desperately searching a renewable energy source, people also put efforts on development of power saving products. For an illumination product, a power saving and environmental friendly light source, that is an LED chip, has been developed. The LED chip generates light by recombination of electrons and holes on a P-N junction. Compared with the conventional light sources, the LED chip has advantages such as low power consumption and long lifespan, and thus has been widely applied in all areas.
The LED chip is a current driven device and needs to be driven by a proper driver circuit. Generally speaking, the LED chip is packaged on a plate having the driver circuit. The method of packaging the LED chip on the plate mainly includes a wire bonding technology and a flip-chip technology. According to the wire bonding technology, the LED chip is mounted upright on the plate by a silver paste or a eutectic technique, and then the LED chip is wire bonded with the bonding pads on the plate by a metal wire. According to the flip-chip technology or referred to as the flip-flop packaging method, the LED chip is mounted with its top surface facing down on the plate by gold balls or a eutectic technique. The eutectic technique evaporates or sputters a layer of eutectic solder on the front or back side of the LED chip. Then, a gold layer is plated on a solder pad of the plate. Afterwards, the plate is placed on a heating board and heated to a melting point of the eutectic solder, then the LED chip is laminated on the solder pad and the gold on the solder pad is bonded with the eutectic solder on the LED chip. Thereafter, the temperature of the plate is lowered below the melting point of the eutectic solder to allow the eutectic solder to be cured, thereby finishing the die bonding process. However, to increase the light utilization efficiency of the LED chip, a metal reflection layer is additionally disposed on the outer layer of the plate in the prior art. When the LED chip is packaged by the above eutectic technique, the metal reflection layer of the plate may be exposed to a high temperature environment and actively reacts with the ambient air with the ambient gas to incur the oxidation problem.